1. Field of the Invention
The present invention relates generally to a sander for smoothening out the ripples and undulations defined along a curved surface. More particularly, the invention concerns a contour sander having sufficient flexibility to conform to the curvature of the surface when a sanding pressure is applied, yet also sufficient hardness to be unimpressionable by the surface ripples and undulations.
2. Discussion of the Prior Art
In various industries, it is often necessary to smoothen a curved surface. For example, the automotive after-market repair industry is continuously involved with the repair of curved body panels. As those of ordinary skill in the art will appreciate, sanding precision and the surface smoothness directly affect the appearance of the repaired panel. That is, surface roughness and deviations from the original shape of the panel are readily visible when a coat of glossy paint is applied to the panel. Of course, such imperfections drastically reduce the aesthetics and resale value of the vehicle. It will be appreciated that repair of curved body panels has recently become especially prevalent as vehicle bodies have become more aerodynamic.
Assuming the damaged body panel is repairable, the repair process typically begins with reshaping the damaged area of the panel back to its basic original configuration with a hammer or pry. The reshaped area of the panel is subsequently covered with a suitable body filler, such as a polyester based putty, for filling depressions in the surface (i.e., the places where the body mechanic was unable to reform the panel back to its original shape). The filler is usually manually smeared onto the reshaped surface of the panel, and consequently, the top surface of the filler presents an undulating or rippled surface. That is, the mechanic is unable to apply a perfectly smooth layer of body filler. Accordingly, the damaged area must be sanded prior to painting. In most cases, smoothening of the area not only involves sanding out the undulations of the body filler but also applying and sanding a suitable primer, such as a lacquer or urethane based primer. Finally, the repaired area may be coated with a desired paint.
The sanding steps of the repair process may be performed a number of ways. If desired, the mechanic may simply grasp a sheet of sandpaper with his or her hands and apply a sanding pressure directly against the back face of the sheet. However, this approach often results in an unevenly sanded surface and is extremely time consuming and tiresome. It is also difficult to maintain the grasp on the sandpaper. Although devices have been developed to facilitate the sanding steps, conventional sanders are problematic, as illustrated in FIGS. 8-10 and described hereinbelow.
FIG. 8 shows a conventional "finish sander", generally designated by the numeral 200, having a foam rubber block 202 and a rubber release pad 204. A sheet of sandpaper (not shown) having a pressure-sensitive adhesive undercoating is releasably attached to the release pad. The finish sander 200 is a relatively soft, "sponge-like" item which can be compressed in virtually any direction, although the pad 204 is more dense and resistant to compression than the foam rubber block 202. Accordingly, when a sanding pressure is applied on the block 202, the sander 200 has the ability to conform generally to the surface curvature of the body filler F, as shown in FIG. 8 (i.e., the upper and lower faces of the sander 200 are normally parallel and substantially flat). However, because of the softness of the sander 200, a bump B projecting from the filler surface indents the bottom of the sander. In other words, the sander 200 is impressionable by undulations defined along the surface of the filler F.
The impressionability of the finish sander 200 poses several problems. For example, because the finish sander 200 follows the undulations of the filler surface, both the ridges and valleys of the surface (the so-called "highs" and "lows") are sanded. As those of ordinary skill in the art will appreciate, the highs must be sanded down before any material is removed from the lows; otherwise, the surface may never be smoothened. In fact, the highs may only become more pronounced if the lows are sanded. Moreover, sanding of the lows will eventually gouge into the surface of the body panel, or create depressions below the original shape of the panel, such that the body filler must be reapplied.
Furthermore, the compressibility of the finish sander 200 makes it very difficult for the user to evenly distribute and control the sanding pressure. The finish sander also fails to provide a comfortable gripping portion for minimizing hand fatigue and slippage from the user's grasp.
FIGS. 9-10 illustrate another prior art sanding device, generally designated by the numeral 300, known as a "file-board sander". The file-board sander 300 includes a base plate 302, a handle 304 and a knob 306. A pair of clips 308 and 310 at either end of the base plate 302 serve to secure a sheet of sandpaper to the base plate. Extending along the top face of the base plate 302 are a plurality of laterally spaced, longitudinal strengthening ribs 312, which serve to rigidify the base plate along its length. As those of ordinary skill in the art will appreciate, the sander 300 is specifically constructed for movement in a longitudinal direction; the sander 300 may roll over if it is moved laterally (i.e., side-to-side). In operation, the user grips the handle 304 with one hand and the knob 306 with the other, applies sanding pressure toward the surface, and moves the sander 300 in a longitudinal direction.
Contrary to the finish sander discussed above, file-board sanders have hard base plates that bridge the lows and contact only the highs of the body filler F (see FIG. 10). However, the base plates of most file-board sanders have virtually no flexibility along the length thereof. Consequently, the base plate cannot conform to the curvature of the surface. Further, only a small portion of the rigid base plate is able to contact the curved surface, and accordingly, the sanding process becomes very time consuming. Moreover, sanding with a rigid base plate tends to create flat areas along the surface such that the repaired panel becomes a plurality of highly visible, small fiats rather than a continuous curve.
The file-board sander 300 shown in FIGS. 9-10 is somewhat exceptional in that the base plate 302 is flexible along a portion of its length, even though the strengthening ribs 312 have been provided to prevent such flexure. Although the handle 304 and knob 306 rigidify the ends of the base plate 302, the flexible portion of the base plate is spaced between the handle and knob, as shown in FIG. 9. This portion conforms generally to the curvature of the body panel P and is unimpressionable by the undulations of the body filler F.
Although the automobile after-market repair body industry has used the sander 300 because of its slight flexibility, this type of file-board sander is problematic. For example, a significant force must be exerted against the sander 300 to flex the base plate 302, which becomes tiresome and tends to result in gouging of the body filler F. Extreme sanding pressures have also been known to clog and tear the sheets of sandpaper. These problems are magnified because the sanding pressure applied against the sander 300 is localized to the small area of the base plate 302 contacting the surface. Furthermore, the sander 300 tends to rock from end-to-end during the sanding process.